1. Field of the Invention
The disclosed apparatus relates to a system for controlling the position of a moveable gun about an axis of rotation, and more particularly to such a system using velocity feedback.
2. Description of the Prior Art
Armed mobile vehicles often have turrets mounted therein which are movable in azimuth and which carry weapons which are movable within the turrets in elevation. In the instance where the weapon is mounted off of the center of rotation in azimuth, the weapon recoil when the weapon is fired will impose a torque about the azimuth rotation axis. Additional torques about the azimuth axis will be imparted to the turret when the counter recoil forces are applied thereto as the breech bolt slams forward into the back of the chamber structure preparatory to firing the ensuing round. Spurious torques may also be experienced about the elevation axis for the weapon as the vehicle rocks on its suspension due to weapon recoil. When an ammunition feed belt is attached to the weapon breech, additional spurious torques about the elevation axis will be imposed due to the feed belt reaction forces.
By way of example, a typical offset, single 20 millimeter turret-mounted weapon carried in an armored vehicle wherein the weapon is capable of being directed in azimuth and elevation will impart 6,000 ft.-lbs. of torque at the turret azimuth ring drive gear for each round fired. This torque level may be substantially overcome in a weapons control system by providing a high reflected drive train inertia to the turret. However, such an approach results in well-known system backlash errors and response time disadvantages. Further, at firing rates of 200 rounds per minute or greater, accumulated error due to the successive recoil torques is unacceptable.
Velocity feedback in control systems is well known. Such a system is seen in U.S. Pat. No. 3,041,518, issued to Blomqvist et al, which relates to a system for controlling the position of a gun barrel to obtain appropriate lead on a target being tracked. In one embodiment described by Blomqvist et al a filter network is provided in the forward control loop which appears to impose a time displacement in the fire control signal provided at the system input in order to provide said firing lead. Blomqvist et al further describe a servo motor for driving the gun mount which is energized by the system output signal and which has an output shaft on which is mounted a gear which meshes with an arc gear attached to the breech ring of the gun barrel. Blomqvist et al do not deal with the critical problem area, relating to relative drive train and driven member inertias together with drive gear ratios, which is so vital in obtaining an acceptable system response.
U.S. Pat. No. 3,456,177 issued to Wilkerson discloses a motor control system which includes tachometer or velocity feedback and also includes an amplifier in the forward portion of the servo loop. The amplifier may include a feedback capacitor which operates to integrate noise signals included in the error signal to thereby reduce instantaneous noise signal values to a level which will not interfere with the control accuracy of the system. A similar system is seen in the U.S. Pat. No. 3,413,534 issued to Stringer.